1. Field of the Invention
The present invention relates generally to motor vehicles, such as passenger cars, light trucks, sport utility vehicles, mini-vans, and other similar vehicles. More particularly, the present invention relates generally to liftgates for such motor vehicles and, even more particularly, to a lightweight, aluminum, and thin profile liftgate for motor vehicles.
2. Description of Related Art
Liftgates are installed in several types of motor vehicles including mini-vans, sport utility vehicles, hatchback cars, and other similar vehicles. They are used most prominently in mini-vans. Liftgates provide access to a rear storage compartment generally found in these vehicles.
Current liftgates are typically assembled from two deep-drawn steel sheet panels and a number of stamped steel sheet reinforcement panels, which are resistance spot-welded to the deep-drawn steel sheet panels. This method of construction utilizes the steel sheet panels primarily to meet required stiffness and strength requirements for the liftgate. Liftgates made by this construction method are thick in cross section, typically measuring five to six (5–6) inches at their thickest point. The thickness of such prior art liftgates takes away from the available cargo space in the rear storage compartment of the vehicle. Additionally, the increased weight of the liftgate made by this construction method makes it difficult to open and close the liftgate, which requires vehicle manufacturers to add various lift assist devices to aid in raising the liftgate. Vehicle manufactures are extremely sensitive to vehicle weight because of government mandates for fuel economy and emissions, which makes the use of heavy liftgates disadvantageous.
The current method of construction for liftgates requires that the latch and other hardware associated with the liftgate be installed on the liftgate by inserting, fastening, and connecting a number of individual components in the cavity defined between the steel sheet panels. Generally, the individual components are assembled through holes punched in the steel sheet panels. This process is difficult, slow, and is error prone, which results in significant repair and warranty costs, and further results in dissatisfied customers. Additionally, the confined and narrow spaces within which the assembly line workers or service technicians must operate occasionally cause injuries to these workers.
A recent development in liftgate design incorporates a flip glass, which may be flipped upward for access to the rear storage compartment without having to lift the heavy liftgate itself. A rear glass wiper motor assembly is typically mounted along the bottom center edge of the flip glass. The flip glass requires a latching mechanism to lock the flip glass to the liftgate. The latching mechanism is also typically mounted along the bottom center edge of the flip glass. A safety brake light is typically mounted along the top center edge of the flip glass. The flip glass design currently used in the automotive industry further requires the use of a second pair of hinges to attach the flip glass to the liftgate, as well as an additional lift assist mechanism for pivoting the flip glass upward to allow access to the rear storage compartment. The current flip glass design known in the art results in a non-smooth surface in the rear of the vehicle, which negatively effects vehicle styling and increases aerodynamic drag. Additionally, this type of construction requires a large window frame, which reduces visibility through the liftgate window. This reduces safety while driving the vehicle, for example, when looking for vehicles approaching from the rear. The reduced visibility is also a significant drawback when backing up the vehicle, for example, while parking the vehicle.
Attempts have been made in the automotive industry to reduce the weight of vehicle body panels by using lighter weight construction materials, such as aluminum and plastic. For example, U.S. Pat. No. 5,449,213 to Kiley et al. discloses an aluminum movable liftgate having a tubular frame located between a pair of inner panels and a pair of outer panels. The frame functions as the load-bearing structure for the liftgate. However, no provision is made in the disclosed liftgate for hardware or for contour and other design preferences for a liftgate installed at the rear of a vehicle. Further, this liftgate does not include flip glass and other design features that are preferred by customers in the marketplace. The disclosure of U.S. Pat. No. 5,449,213 to Kiley et al. is incorporated herein by reference.
Another example of an attempt to reduce the weight of vehicle body panels is disclosed in U.S. Pat. No. 6,003,931 to Dancasius et al. This reference discloses a swiveling or sliding hatchback for a vehicle that incorporates materials having lower weight to reduce the overall weight of the hatchback. The hatchback includes a continuous frame element and inner and outer skins mounted on the frame element. The inner and outer skins are formed of light metal or plastic and are reinforced with reinforcing ribs.
A further example of the trend toward reducing the weight of vehicle body panels is disclosed in U.S. patent application Publication No. 2002/0046505A1 to Seksaria et al., the disclosure of which is incorporated herein by reference. This publication discloses a sliding door for a mini-van that is comprised of a rectangular shaped space frame and inner and outer door panels attached to the space frame. Hardware for operation of the sliding door is mounted on the exposed inside surface of the sliding door.
Accordingly, a need remains for a thin, lightweight liftgate that maximizes vehicle interior space but also allows ready access to the rear storage compartment in a vehicle such as a mini-van, sport utility vehicle, hatchback car, and other similar vehicles.